1. Field of the Invention
The present invention relates to a thermal recording material, and particularly to a thermal recording material that places a small burden on the environment, high in sensitivity and superior in background fogging, image preservability, resistance to inkjet inks, chemical resistance and adaptability to inkjet printing. Further, the invention relates to a thermal recording material, and particularly to a thermal recording material that is high in sensitivity and superior in background fogging, image preservability, chemical resistance, thermal head matching characteristics (such as adhesion of scum to thermal head and abrasion properties of thermal head) and resistance to inkjet inks. Moreover, the invention relates to a thermal recording material, and particularly to a thermal recording material that is high in color density and superior in background fogging, image preservability and chemical resistance and is provided with adaptability to inkjet recording and adaptability to head scum.
2. Description of the Related Art
Since thermal recording materials are relatively inexpensive, and recording instruments thereof are compact and free from maintenance, the thermal recording materials are broadly used. And, in order to enhance the color density and image preservability of thermal recording materials, not only development of electron-donating colorless dyes and electron-accepting compounds but also study about the layer structure of thermal recording materials are being extensively carried out.
In recent years, a sales competition of heat-sensitive paper intensifies, and thermal recording materials are required to have higher functions that can be differentiated from the conventional functions. Accordingly, the thermal recording materials are extensively studied with respect to color density, image preservability, and the like.
In the conventional thermal recording materials, 2,2-bis(4-hydroxyphenyl)propane (bisphenol A or BPA) has been widely used as an electron-accepting compound against electron-donating colorless dyes to be used. However, satisfactory properties have not been obtained from the viewpoint of sensitivity, background fogging, image preservability, and so on.
On the other hand, JP-B No. 4-20792 discloses that recording materials using an N-substituted sulfamoylphenol or N-substituted sulfamoylnaphthol as the electron-accepting compound improve image density, image stability, cost, etc. of the (pressure-sensitive or heat-sensitive) recording materials. However, there is room for further improvements in the image density and image preservability.
In recent years, from an increase of consciousness to the environment, a demand of thermal recording materials using a support composed mainly of waste paper pulp (so-called “recycled paper”) is rising. However, when recycled paper is used as a support, the background fogging and image preservability become worse, and satisfactory thermal recording materials have not always been obtained. In particular, when the above mentioned BPA is used as a color developer in the generated paper, the background fogging and image preservability become worse.
As the thermal recording materials using recycled paper, JP-A No. 3-140287 describes a thermal recording material using a phenol-based color developer (including bisphenol-based color developers), a sulfone-based color developer, or a hydroxybenzoic acid-based color developer, in which recycled paper having a measured value of 8% or more by a regular reflection type smoothness sensor under a pressure condition of 20 kg/cm2 in terms of original paper surface is used, thereby improving the recording sensitivity without generation of background stains, resulting in enabling to make it correspond to super high-speed machines. However, such a thermal recording material is not satisfactory in image preservability.
JP-A No. 4-21486 describes a thermal recording material having a good color re-developing performance (color-developing properties after preservation) even when recycled paper is used as the support, in which bis(4-hydroxyphenyl)acetate-n-butyl, 4-hydroxy-4-isopropoxy-diphenylsulfone, 4,4′-thiobis(3-methyl-6-tert-butylphenol), or N,N′-diphenyl thiourea is used as a color developer. However, the thermal recording material described in this patent document is not satisfactory in background fogging and image preservability.
Further, in recent years, inkjet prints become widespread as output applications from personal computers, and there is often seen in offices and so on the state where the recording surfaces of inkjet recording materials and those of thermal recording materials are placed overlaid each other. There occur problems of a fog of the background portion of the thermal recording material and a reduction in density of image portions in the conventional thermal recording materials, when the recording surface of the thermal recording material is brought into contact with the recording surface of the inkjet recording material, since the conventional thermal recording materials do not have enough resistance against inkjet inks.
In addition, when full-color information is recorded on thermal recording materials, recording using inkjet inks is often employed. When inkjet printing is performed on usual thermal recording materials, there may be the case where colors of the inks are not precisely reproduced, and vivid colors do not appear, whereby the resulting colors become dull. And, when inkjet recording is performed on the thermal recording material described in JP-B No. 4-20792, there is a problem that the colors are dull and blackish.